The present invention relates generally to wireless communication systems and, in particular, to wireless communication employing transmit diversity.
Several third generation wireless communication systems are being developed. One such third generation wireless communication system is known as CDMA 2000. In CDMA 2000, a variety of techniques are being incorporated for improving call quality. Open loop transmit diversity is one such technique in which user signals are transmitted using two antennas. In a first phase of CDMA 2000, open loop transmit diversity is currently being implemented in a form of orthogonal transmit diversity (OTD). In OTD, separate antennas are used to transmit even data bits and odd data bits to achieve transmit diversity and improved call quality.
In a second phase of CDMA 2000, open loop transmit diversity may be implemented in a form of space time spreading (STS) using Walsh functions or codes. STS enhances call quality by providing variable gain over OTD depending on the coding rate being used. Specifically, in STS, odd data bits and even data bits are jointly, not separately, transmitted over two antennas. However, the manner in which the odd and even data bits are modulated/processed before being transmitted over one antenna will be different from the manner in which the odd and even data bits are modulated/processed being transmitted over the other antenna.
There has been some concern that including both open loop transmit diversity schemes as options in CDMA 2000 would be very complex in terms of implementing them into a common transmitter architecture. Accordingly, there exists a need for a simple way to implement common transmitter architecture that has incorporated orthogonal transmit diversity and space time spreading schemes.
The present invention is a common transmitter architecture having incorporated both open loop transmit diversity schemes using a plurality of binary switches. Employment of binary switches allows for the sharing of certain components whether the transmitter is utilizing a orthogonal transmit diversity (OTD) scheme or a space time spreading (STS) scheme. Accordingly, the number of components in the transmitter is minimized and the complexity of the transmitter is simple enough to be implemented into a single application specific integrated chip.
The transmitter has an OTD and a STS mode, and comprises a first and second antenna system. The first antenna system comprises time multiplexers, mixers, switches and adders. The time multiplexers are used to time multiplex an in-phase first signal with a second in-phase first signal to produce a first time multiplexed signal; a quadrature phase first signal with a second quadrature phase first signal to produce a second time multiplexed signal; an in-phase second signal with an inverted in-phase second signal to produce a third time multiplexed signal; and a quadrature phase second signal with an inverted quadrature phase second signal to produce a fourth time multiplexed signal. The mixers are used to mix outputs of the time multiplexers with a Walsh function to produce first, second, third and fourth mixed time multiplexed signals. The first and second time multiplexed signals are directed to the adders. If the transmitter is in STS mode, the switches direct the third and fourth mixed time multiplexed signals to the adders so they may be added with the first and second mixed time multiplexed signals, respectively. If the transmitter is in OTD mode, the switches do not direct the third and fourth mixed time multiplexed signals to the adders.
The second antenna system comprises time multiplexers, mixers, switches and adders. The time multiplexers are used to time multiplex an in-phase second signal with an inverted in-phase second signal when the transmitter is in the first operating mode and with an in-phase second signal when the transmitter is in the second operating mode to produce a fifth time multiplexed signal; a quadrature phase second signal with an inverted quadrature phase second signal when the transmitter is in the first operating mode and with a quadrature phase second signal when the transmitter is in the second operating mode to produce a sixth time multiplexed signal; an in-phase first signal with an inverted in-phase first signal to produce a seventh time multiplexed signal; and a quadrature phase first signal with an inverted quadrature phase first signal to produce an eighth time multiplexed signal. The mixers are used to mix outputs of the time multiplexers with a Walsh function to produce fifth, sixth, seventh and eighth mixed time multiplexed signals. The fifth and sixth time multiplexed signals are directed to the adders. If the transmitter is in STS mode, the switches direct the seventh and eighth mixed time multiplexed signals to the adders so they may be added with the fifth and sixth mixed time multiplexed signals, respectively. If the transmitter is in OTD mode, the switches do not direct the seventh and eighth mixed time multiplexed signals to the adders.